Gupta et al. BMC Genomics (2015) 16:540 DOI 10.1186/s12864-015-1748-1 RESEARCHARTICLE Open Access Scrutinizing the immune defence inventory of Camponotus floridanus applying total transcriptome sequencing Shishir K. Gupta1,2†, Maria Kupper2†, Carolin Ratzka2†, Heike Feldhaar3, Andreas Vilcinskas4, Roy Gross2*, Thomas Dandekar1,5* and Frank Förster1 Abstract Background: Defence mechanisms of organisms are shaped by their lifestyle, environment and pathogen pressure. Carpenter ants are social insects which live in huge colonies comprising genetically closely related individuals in high densities within nests. This lifestyle potentially facilitates the rapid spread of pathogens between individuals. In concert with their innate immune system, social insects may apply external immune defences to manipulate the microbial community among individuals and within nests. Additionally, carpenter ants carry a mutualistic intracellular and obligate endosymbiotic bacterium, possibly maintained and regulated by the innate immune system. Thus, different selective forces could shape internal immune defences of Camponotus floridanus. Results: The immune gene repertoire of C. floridanus was investigated by re-evaluating its genome sequence combined with a full transcriptome analysis of immune challenged and control animals using Illumina sequencing. The genome was re-annotated by mapping transcriptome reads and masking repeats. A total of 978 protein sequences were characterised further by annotating functional domains, leading to a change in their original annotation regarding function and domain composition in about 8 % of all proteins. Based on homology analysis with key components of major immune pathways of insects, the C. floridanus immune-related genes were compared to those of Drosophila melanogaster, Apis mellifera, and other hymenoptera. This analysis revealed that overall the immune system of carpenter ants comprises many components found in these insects. In addition, several C. floridanus specific genes of yet unknown functions but which are strongly induced after immune challenge were discovered. In contrast to solitary insects like Drosophila or the hymenopteran Nasonia vitripennis, the number of genes encoding pattern recognition receptors specific for bacterial peptidoglycan (PGN) and a variety of known antimicrobial peptide (AMP) genes is lower in C. floridanus. The comparative analysis of gene expression post immune-challenge in different developmental stages of C. floridanus suggests a stronger induction of immune gene expression in larvae in comparison to adults. Conclusions: The comparison of the immune system of C. floridanus with that of other insects revealed the presence of a broad immune repertoire. However, the relatively low number of PGN recognition proteins and AMPs, the identification of Camponotus specific putative immune genes, and stage specific differences in immune gene regulation reflects Camponotus specific evolution including adaptations to its lifestyle. Keywords: Camponotus floridanus, Carpenter ant, Transcriptome, Re-annotation, Immune system * Correspondence: [email protected]; dandekar@ biozentrum.uni-wuerzburg.de †Equal contributors 2Department of Microbiology, Biocentre, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany 1Department of Bioinformatics, Biocentre, University of Würzburg, Am Hubland, D-97074 Würzburg, Germany Full list of author information is available at the end of the article © 2015 Gupta et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Gupta et al. BMC Genomics (2015) 16:540 Page 2 of 21 Background insect [2]. For example, Le Conte and co-workers dis- Insects are among the most successful animal life forms covered several genes which might contribute to social on Earth in terms of species richness and abundance. immunity in honey bees [11]. A striking new finding Like all other living organisms they are under permanent was reported recently for the closely related ant C. threat of infection by harmful microorganisms. pennsylvanicus, in which a Cathepsin D like protease Insects are not endowed with an adaptive immune sys- was found to be transmitted to other ants by trophallaxis, tem and must rely entirely on innate immune mechanisms leading to an increased infection resistance in the recipients or externally applied immune defences [1, 2]. Invading mi- [12]. The first genome sequence of a social insect, the croorganisms that break the primary passive protective honey bee, revealed an apparently low number of genes barriers such as the cuticle or the peritrophic membrane with immune-related functions as compared to solitary in the gut encounter immediate-acting defence strategies insects [13]. Accordingly, it was suggested that external such as phagocytic cells, phenoloxidase activity and react- immune defences including social immunity may have ive oxygen species. As a second line of defence a powerful alleviated selection pressure from the canonical innate antimicrobial immune response is mounted, mainly based immune factors as internal and external immune de- on AMPs but also including serine proteases, stress factors fences may trade off against each other. However, the and factors involved in opsonisation and clotting [3, 4]. recent honey bee genome upgrade identified about 5000 Based on several structural features, the AMPs can be more protein encoding genes than previously reported, classified into several groups such as α-helical peptides, which need to be analysed carefully in the future [14]. In glycine-rich peptides, cysteine-rich peptides or proline- addition, the genome sequences of several other hymen- rich peptides [5]. opteran and dipteran species reveal that dipterans appear Detection of microbial invaders is achieved by pattern to have an unusually high number of immune genes and recognition receptors (PRRs) which recognise conserved that a social lifestyle may not directly correlate with this structural motifs of the microorganisms such as DAP- number [15]. or Lys-containing PGN of respectively Gram-negative or A specific feature of C. floridanus is its obligate inter- Gram-positive bacteria [4]. The conserved molecular action with an intracellular mutualistic y-Proteobacterium, patterns of the microbes they recognise are called mi- Blochmannia floridanus, which resides in midgut cells and crobe associated molecular patterns (MAMPs) [6]. These in the ovaries and supplements nutrients to its host [16]. PRRs then interact with cellular signalling systems such The host recognises the endosymbiont as non-self and the as Toll, IMD, Jak-Stat, and JNK pathways, which ultim- immune system can therefore play a role in maintenance ately lead to the activation of an immune response [7, 8]. and regulation of the chronic infection by the endosymbi- Early work on the Drosophila melanogaster immune sys- ont [17], while on the other side it has to defeat patho- tem already revealed striking similarities of these signal genic microorganisms, thus possibly requiring specific transduction pathways with those of vertebrates. For in- adaptations of its immune system [18]. For instance, stance, the identification of the Drosophila Toll receptor previous work revealed a localised down-modulation was a milestone discovery, since later it was found that of the immune response that is restricted to the midgut related PRRs of vertebrates, the so-called Toll-like re- tissue of the ants and correlates with massive replication ceptors, also play a dominant role in the innate immune of the endosymbiont in this tissue [18]. system of vertebrates [8]. To get insight into the immune system of the carpen- Here we characterise the immune system of the car- ter ant and to unravel possible specific adaptations to its penter ant C. floridanus. These ants live in huge colonies lifestyle as a social insect living in an obligate mutualistic of genetically highly related animals. The high density interaction with a bacterial endosymbiont, we re-evaluated of closely related individuals within the nest may pose the data available from the recently published genomic specific hygiene problems since pathogen transfer may sequence of C. floridanus [19] and extended this dataset be facilitated by the close contact of colony members. with genome-wide transcriptome data generated from On the other hand, social insects have evolved many animals with or without previous immune challenge. additional hygienic measures on the colony level which To identify and functionally annotate the key players may improve health of the individuals, such as cleaning of the C. floridanus immune response and to determine behaviours or the use of other external immune defences the interactions among these players, we performed a de- such as the application of antimicrobial secretions, a tailed analysis including sequence and domain analysis phenomenon termed ‘social immunity’ [2,9,10].Thus, and pathway annotation (including signalogs [20]). Trans- not only the canonical genes encoding AMPs or factors ferring annotation of proteins at a domain level allows involved in signalling pathways but also